Field of the Invention
The present invention relates to a driving force transmission apparatus, a sheet conveyance apparatus including the driving force transmission apparatus, and to an image forming apparatus including the driving force transmission apparatus.
Description of the Related Art
The image forming apparatus includes a plurality of conveyance rollers configured to convey sheets, and a conveyance roller drive mechanism configured to drive those conveyance rollers. With use of those conveyance rollers, the sheets are conveyed from a sheet receiving cassette or a sheet stacking tray sequentially to an image forming unit configured to form images, and to a sheet delivery tray.
Further, there is given another type of image forming apparatus including a standard or optional conveyance unit configured to convey the sheets with their front and back surfaces being inverted to each other so as to perform duplex printing involving image formation on both a first surface and a second surface of each of the sheets.
In the conveyance unit of various types of apparatus, an operation of switching a forward rotation direction and a reverse rotation direction of the conveyance rollers to each other is performed so that the sheet that has already been subjected to printing on its first surface is switched back and fed into the image forming unit again for printing on its second surface.
In this context, the rotation directions of the conveyance rollers are switched by performing control to switch rotation directions of a motor configured to drive the conveyance rollers, or switched with use of a reverse drive mechanism as disclosed in Japanese Patent Application Laid-Open No. 2011-140980. In the method as disclosed in Japanese Patent Application Laid-Open No. 2011-140980, the image forming apparatus need not include a dedicated motor for the conveyance rollers to be subjected to switching between a forward rotation and a reverse rotation, and hence the image forming apparatus can be relatively inexpensively manufactured.
However, in a conveyance roller drive mechanism used in the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2011-140980, as illustrated in FIG. 13 of the present invention, in a pair of planetary gear mechanisms 104 and 105 to be used in combination with each other, only sun gears 100 and 101 including projecting portions need to be formed into different shapes. Specifically, tooth profiles of the projecting portions of the sun gears 100 and 101 of the planetary gear mechanisms are inverted to each other as illustrated in FIG. 13. The reason is as follows.
Specifically, as illustrated in FIG. 13, rotation directions J1 and J2 of the pair of planetary gear mechanisms 104 and 105 are reverse to each other. Distal ends of an engaging arm 102 that is pivotable about a shaft by a solenoid 103 are engaged with the sun gears 100 and 101 of the planetary gear mechanisms. When the distal ends of the engaging arm 102 are selectively engaged with the sun gears in this way, rotation of any one of the planetary gear mechanisms 104 and 105 can be stopped. For this reason, as described above, the tooth profiles of the projecting portions of the sun gears 100 and 101 of the planetary gear mechanisms are inverted to each other.
Thus, the pair of planetary gear mechanisms are not mountable compatibly with each other, and hence operators need to take great care not to make a mistake in assembly of the apparatus. Further, in addition to reduction in assembly work efficiency due to the above-mentioned problem, there are problems of a manufacturing cost for a die set for forming the inverted tooth profiles of the projecting portions of the sun gears as described above, a management cost for components, and the like.
Still further, in a case where the planetary gear mechanisms are further downsized, an interval between the projecting portions inevitably decreases, which leads to a difficulty in arranging the engaging arm.
Yet further, in a case where the projecting portions of the pair of planetary gear mechanisms are formed into the same shape, as illustrated in FIG. 14 of the present invention, the force F in a direction of disengaging an engaging arm 107 is generated in a projecting portion 106 on one side. In order to counteract this push-out force F, for example, a tension spring 108 may be used to apply an urging force to the engaging arm 107. However, in order to switch positions of the engaging arm 107, a driving force greater than a force of the spring needs to be applied. Thus, there may be caused another problem of an upsizing of a switching actuator such as the solenoid.